South Korea's Defence Ministry says, North Korea is ready to conduct an additional nuclear test at any time, three days after the reclusive North's fifth test drew widespread condemnation. <br/><br/>Pyongyang set off its most powerful nuclear blast to date on Friday, saying it had mastered the ability to mount a warhead on a ballistic missile and ratcheting up a threat that its rivals and the United Nations have been powerless to contain.<br/><br/>South Korea's President Park Geun-hye said later that North Korea's nuclear weapons and missiles posed an imminent threat, as tensions rose on the Korean peninsula in the wake of the test last week.